The study was done to further explore the pharmacokinetic effects of gemcitabine and cisplatin on each other. Twelve patients with stage IIIb or IV advanced non small cell lung cancer, whose cancer could not be cured with surgery or radiation, and who had not received chemotherapy before were scheduled to participate in the study. Thirteen blood samples per patient were drawn over one 24-hour period on the GCRC in-patient unit. If other scheduled draws occurred on weekends, these were also done on the GCRC outpatient unit.